Simulink Control Design™ - MathWorks

If safe operation of your plant is not a practical concern (such as when tuning against a

plant model in Simulink), open-loop autotuning has these advantages:

• Open-loop tuning can result in more accurate frequency-response estimation and
  tuning. In closed-loop tuning, the controller suppresses injected perturbations, which
  can result in less accurate frequency-response estimation and poorer tuning results.


• Open-loop tuning is faster. Closed-loop tuning uses a lower-frequency perturbation
  signal, which makes the process about three times longer.


• The memory footprint of the deployed algorithm is slightly smaller.

Caution

• Do not use either closed-loop or open-loop PID autotuning with an unstable plant.


• Do not use open-loop PID autotuning with a plant that has more than one integrator.
  You can use closed-loop PID autotuning with a multiple-integrator plant.

To get started with either type of PID autotuner, see “How PID Autotuning Works” on

page 8-6.

When Not to Use PID Autotuning

PID Autotuning is not suitable for unstable plants. The perturbations applied in open-loop

tuning can drive an unstable plant to operating conditions that are unsafe for the plant.

Although closed-loop autotuning does not have that risk, it does not yield meaningful

tuning results for unstable plants.

PID autotuning does not work well when there are large disturbances in the plant during

the estimation experiment. Disturbances distort the plant response to the perturbation

signals, yielding poor estimation results.

See Also

Closed-Loop PID Autotuner | Open-Loop PID Autotuner

8 PID Autotuning